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The protein is found in the nucleus of the cell and is bound to the DNA. When working correctly the protein regulates cell division so that tumours dont form. It also has another very important role. Let's say for instance that the cells have been exposed to radiation or burns to the extent that DNA has been damaged. The protein has the very important role of deciding whether the DNA can be repaired or whether the cell has to go through the process of apoptosis (programmed cell death). This example alone shows the importance of this gene working correctly so that transcription works correctly to produce the proper protein and so begs the question "How does this relate to breast cancer?" Well there are a few answers to that question. One result of a defective TP53 gene is Li-Fraumeni syndrome. Any cell that has this type of defective TP53 gene has a far greater risk of contracting cancer "Individuals with LFS have up to a 50% chance of developing cancer by age 40 and a 90% chance to develop cancer by age 60. Breast cancer appears to be the greatest risk for women. However, less than 1% of all breast cancer is thought to be related to LFS."  Another cause of breast cancer by a defective TP53 gene is caused by the somatic mutations which account for "20% to 30% of all breast cancer cases"  . The usual cause is that an abnormal amino acid is produced in the protein chain which makes the protein ineffective and therefore causes the cell to grow and divide erratically. The same symptoms can be noticed if the TP53 gene is absent in a cell.
Phosphatase and tensin homolog (PTEN) is a very important gene that produces a protein found in nearly all tissue. The PTEN protein is an enzyme that modifies fats and other proteins by removing phosphate groups.
PTEN gene location on the chromosome
When working correctly the enzyme, created by the PTEN gene, is involved in the chemical pathway which signals apoptosis (programmed cell death). PTEN is also thought to help in the control of cell adhesion, cell migration and angiogenesis. Once again the question of how this gene relates to breast cancer. All of the roles of the enzyme created by this gene add up to a key tumour suppressor as all are involved in cell proliferation in some way. The main cancerous danger of this gene is caused by somatic mutations that change the gene, this results in a defective enzyme being produced. This defective enzyme is not able to control cell proliferation as it should and therefore cancerous cells can be allowed to reproduce and grow at an uncontrollable rate.
Serine/threonine kinase 11 (STK11) gene creates a protein that acts as a tumour suppressor.
STK11 gene location on the chromosome
The enzyme stops the cell from reproducing irregularly and is also another link in the promotion of the process known as apoptosis (programmed cell death). Another useful role by this enzyme when the gene is working correctly is the polarisation effects it has on cells e.g. it assists in the orientation of cells in tissue. The protein also controls how much energy is used by the cell. All these are key control elements in tumour suppression. Mutations in this gene cause Peutz-Jeghers syndrome. Over 140 different mutations  of the STK11 gene have been reported to cause this syndrome. Mutations usually create a shorter non functioning version of the enzyme and studies show that when the enzyme isn't functioning properly the cell divides to quickly and polyps are formed which sometimes develop into cancerous tumours. With the defective enzyme comes as a far larger risk of breast cancer. Only a small percentage of breast cancers are actually related to Peutz-Jeghers syndrome which are usually inherited. It's even rarer for breast cancer to be caused by somatic mutations in this gene but it has happened. Cells tend to uncontrollably divide which in turn leads to malignant growths.
Cadherin 1, E-cadherin (epithelial) (CDH1) is responsible for the production of the protein E-cadherin.
CDH1 gene location on the chromosome
Cadherins are proteins that bind cells together (cell adhesion) to form tissues. They are calcium dependent which means they require the presence of calcium to perform properly. In addition to cell adhesion E-cadherins have some very important roles which include the transmition of chemical messengers from cell to cell, control of cell movement and control of selected genetic behaviour. Studies suggest that CDH1 is a tumour suppressor gene which helps regulate cell proliferation and stop cancerous tumours from growing. Also because cadherins help cells stick together it is thought that they stop cancerous cells from breaking free and entering the blood stream which limits the spread of cancer to other tissues (metastisizing). There is an increased risk of breast cancer when the CDH1 gene is mutated. Inherited mutations of the CDH1 gene increase the risk of lobular breast cancer that begins in the mammary glands. Somatic mutations of this gene are common but so are damages to the DNA that calls upon the gene. It is thought that the genetic mutations lead to uncontrollable division and growth of the cells. Also the lack of E-cadherins, through errors in its synthesis, can lead to cancerous cells metastisizing to other parts of the body.
Checkpoint kinase 2 (CHECK2) is the gene responsible for the synthesis of the protein checkpoint kinase 2.
CHEK2 gene location on chromosome
The protein itself acts as a tumour suppressor. This means that it controls the cells proliferation. The protein becomes active when DNA becomes damaged in the cell. Cell division is then halted and CHEK2 then interacts with other proteins such PT53 to see if the DNA can be repaired or if the cell should be destroyed through the process of apoptosis. Damages can easily happen through exposure to things such as toxic chemicals, UV rays from the sunlight, radiation burns etc. Another way that DNA can break is through the daily genetic processes that get carried out. Mutations in this gene slightly increase the risk of breast cancer. The most known dangerous mutation is the deletion of a nucleotide at the position 1100 in the CHEK2 gene. This creates a shortened version of the protein that is ineffective in its tumour suppressor role. Cells are allowed to divide and grow uncontrollably which can then lead to cancerous tumours in the breasts. There are also links to Li-Fraumeni syndrome from mutations of this gene but it is known whether this gene is a cause or a result of the syndrome.
Ataxia telangiectasia mutated (ATM) is a very interesting gene. Its responsible for the synthesis of a protein that is located in the nucleus of cells. Its primary role is to control the growth and division of cells but it also plays a large role in the growth of the nervous system and the immune system.
ATM gene location on the chromosone
The ATM gene is located on the long (q) arm of chromosome 11 between positions 22 and 23.
The ATM protein plays a main role in DNA damage recognition and repair. It activates the enzyme required to fic the broken strands. These strands can become broken through daily tasks such as cell division where the information in the DNA is called upon. Other damages to be repaired may once again result from external sources like radiation, damage from UV rays and burns. In relation to breast cancer there seems to be three forms of instances when it comes to ATM. The first is the mutation of one of the genes in each cell. This creates an ineffective protein that hinders the performance of the control of cell proliferation and DNA repair which in return leads to cancerous tumours. The second instance is the deletion of the gene which mean the cells only hold one copy of the gene which therefore means that only half the amount of the required protein is synthesised. This leads to an ineffective control of cell proliferation and DNA repair which in turn can also lead to a higher risk in breast cancer. In the third instance both ATM genes in the cell have mutated and they form a short ineffective protein that doesnt function properly. This is known as ataxia-telangiectasia. When the ATM protein is not working the cell becomes very sensitised towards radiation and things like UV rays. Other genes in the cell become damaged and mutated as a result of the missing protein and this can lead to cancerous tumours.
MutL homolog 1 (MLH1) is a gene that produces a remarkable protein involved in the repair of DNA. The gene belongs to a group called the mismatch repair genes. Basically the protein created by this gene is an essential part in the process that corrects wrongly produced DNA strands. If a DNA strand is created during DNA replication and a part of it has the wrong code then this protein, paired with the PMS2 protein, removes the wrongly created part and replaces it with the correct order of bases. Mutations in this gene can cause a disorder known as Lynch syndrome. When these genes are mutated an effective protein is produced which leads to a build-up of wrongly coded DNA. This wrongly coded DNA can lead to uncontrolled cell proliferation which can then lead to an increased risk of cancerous tumours in the breasts.
MLH1 gene location on the chromosome
The MLH1 gene is located on the short (p) arm of chromosome 3 at position 21.3.